Abstract Currently, there are no molecular probes that are specifically designed for quantitative imaging of articular cartilage health. In osteoarthritis (OA), the articular cartilage becomes degraded with loss of glycosaminoglycans (GAGs) from the cartilage matrix serving as an early biomarker of the disease process. As such, there are clinical opportunities to mitigate cartilage damage in patients if OA is identified in its earliest stages. Ionic Pharmaceuticals is developing a novel cationic CT contrast agent for targeted quantitative imaging of changes in GAG content and mechanical properties of articular cartilage. Recent data demonstrates that the cationic contrast agent (CA4+) is more sensitive at imaging ex vivo and in vivo articular cartilage than currently available commercial anionic contrast agents. This superior performance of the cationic contrast agent is attributed to the electrostatic attraction between the cationic contrast agent and the negatively-charged GAGs present in articular cartilage. Two critical steps towards commercialization of this technology and the use of this contrast agent in the clinic are addressed in this proposal: 1) GMP synthetic scale-up, necessitated by subsequent pharmacokinetics studies; and 2) Characterization of the interaction between CA4+ and GAGs along with the capability of CA4+ to quantify GAG and mechanical properties in human articular cartilage. Thus, the specific aims of this proposal are: Specific Aim 1: GMP Synthesis of CA4+ (500 g) and establishment of analytical methods. Specific Aim 2: Characterize the interaction between the CA4+ and glycosaminoglycans found in human articular cartilage tissue and determine the correlations between CECT attenuation, GAG content, and cartilage mechanical properties.